Extracts prepared from Ginkgo biloba have been used in medicine since 1965 for the treatment of disturbances of cerebral and peripheral arterial blood flow; see German Pat. Nos. 17 67 098 and 21 17 429. These extracts are called monoextracts (see S. S. Chatterjee and G. Trunzler, Arztezeitschrift fur Naturheilverfahren 22 (1981), 593 to 604). They contain flavone glycosides as the main constituent.
The isolation of a lactone compound having the molecular formula C.sub.15 H.sub.18 O.sub.8 from the leaves of Ginkgo biloba was first mentioned in 1967 by R. T. Major (Science 157 (1967), 1270 to 1273). The physicochemical properties of this compound and derivatives were described, and the name bilobalide was proposed, by K. Weinges and W. Bahr (Liebigs Ann. Chem. 724 (1969), 214 to 216). The following structural formula I was proposed for bilobalide in a combined publication by the groups of K. Nakanishi et al., R. T. Major et al. and K. Weinges et al. (J. Amer. Chem. Soc. 93 (1971), 3544 to 3546) ##STR1##
No medicinal effects of bilobalide have been disclosed. However, it is known that bilobalide has no fungicidal action on Monilia fructicola and Penicillium glaucum nor any bactericidal action on Escherichia coli. Moreover, it is known that bilobalide has no inflammatory action on the mouse ear.
Investigations have shown that the known monoextracts only contain negligible amounts of bilobalide.
Clinical investigations have now surprisingly shown that the Ginkgo biloba extract substance bilobalide has favourable effects on existent neuropathies, neurological and mental functions. It was furthermore shown that monoextracts which were prepared in such a manner that they retain the natural content of bilobalide of Ginkgo biloba or to which bilobalide is added show in addition to the therapy of disturbances of blood flow the above mentioned favourable effects on existent neuropathies, neurological and mental functions. To date, these actions have been attributed exclusively to the demonstrated actions of the monoextract in promoting blood flow. However, pharmacological investiations have shown that the bilobalide-containing monoextracts possess additional properties which go beyond the promotion of blood flow, and which might be responsible for the improvements in nervous diseases observed clinically.